Photos have surfaced on Twitter of smiling men celebrating in front of airplanes, alleged to be images of the capture of Tripoli’s airport by jihadist forces. The seizure of the Libyan capital’s airport–and eleven of its commercial jetliners–has caused concern that the Islamists will use the planes for an attack on September 11.

The Daily Mail highlights a series of photos from virulently pro-Muammar Qaddafi tweeter @Volksbüro which appears to show celebrations at Tripoli airport after the defeat of the Libyan army. Showcasing images of the men at the airport, the Twitter user tweets:

The jihadist group’s behavior echoes that of another group of militia fighters who captured a U.S. embassy annex in the Libyan capital, then posted photos of themselves online enjoying a dip in the building’s swimming pool.

News of the missing jetliners from Tripoli airport first surfaced in the North African online newspaper Magharebia, where a reporter wrote in Arabic, “Libya is now a source of danger not only for neighbouring Maghreb countries, but for all countries of the world.” As the anniversary of both the September 11, 2001, attacks on America and the attack on the Benghazi consulate in Libya approaches, concerns have escalated as to what the jihadists militias are capable of, given the destructive properties of commercial jetliners in the hands of terrorists.

It is not yet clear which jihadist groups are in control of the planes. There is also no information about where the planes are being kept or who is in control of them. The fighters pictured in the photos disseminated on Twitter, the Daily Mail notes, are believed to be members of the group Libyan Dawn. They are not the only terrorist group operating in Tripoli. According to Moroccan military expert Abderrahmane Mekkaoui, who spoke to Al Jazeera television, the planes are in the custody of a group called the Masked Men Brigade, though this report remains unconfirmed.

Ansar al-Sharia, the group believed to have been involved in the attack on the Benghazi consulate, is also operating in the capital. While they have known ties to the Islamic State, the Middle Eastern terrorist group, Libyan Dawn is believed to work exclusively with al-Qaeda, from which the Islamic State split.